Abstract

We have shown that the decay of the photoexcited carrier after termination of disequilibrating illumination follows the stretched-exponential-relaxation law $n(t) = n(0) exp[ - (t/\tau)^{\beta}]$. It is found that the stretching parameter $\beta$and relaxation time constant z depend on temperature with \beta ranging from 0.2 to 0.4. The stretched exponential relaxation is attributed to the capture-enhanced motion of an Si donor atom from the substitutional to an interstitial site in an $Al_xGa_{1-x}As$ lattice during the capture of photoexcited electrons from the conduction band.Temperature-dependent $\beta$ is associated with the distribution of activation energies due to local atomic alloy disorder in $Al_xGa_{1-x}As$. The distribution of activation energies is also verified with the novel spectroscopic technique based on deep-level transient spectroscopy.